I hope this user review helps anyone interested in the Canon ST-E2 Transmitter.

WHAT IS THE ST-E2?

It is a master unit that tells remote Canon Speedlites when and how to fire. It reads the data provided by the remote Speedlite pre-flashes and relays the information to the camera in order to set the correct exposure. It has four independent channels, so if you're working near other photographers, you can work on different channels.

It slides onto the hot shoe and is used to wirelessly control Canon Speedlites. Each channel can control two groups of flashes. You can set each group to E-TTL mode or manual in order to suit your requirements. With E-TTL, the camera gets most of its metering information from the ST-E2/Speedlites. The camera also uses data from the lens, such as distance information and f-stop values.

The transmission range is 8 metres outdoors (and the flash can illuminate a subject up to a further 2m away, so the effective distance is actually 10 metres outdoors) and 12 metres indoors (and the flash can illuminate a subject uo to a further 3m away, so the effective distance is actually 15m indoors).

Also, in low-light conditions, the built-in AF-assist beam is automatically emitted to make it easier for the camera to autofocus from 60cm up to 10 metres.

WHAT'S IN THE BOX?

Apart from the transmitter itself, there's a soft carrying pouch, two multi-language Instruction Manuals and a Warranty Card. But it's what isn't in the box that's surprising - a battery! Despite the high price, the transmitter doesn't come with a battery so you'll also need to buy a 2CR5 battery to get started:

SETTING UP THE ST-E2

Here's a picture of the transmitter attached to my Canon EOS-450D and, as you can see, it's quite large:

To set up the transmitter, (a) attach it to the camera hot shoe, (b) turn it on using the power switch, (c) select the proper channel using the channel button (default is 1) and the number will be lit, (d) to turn on the ratio feature press the ratio button, (e) adjust the flash ratio settings using the left and right arrow buttons, and (f) turn on hugh speed sync by pressing the button with the flash symbol next to an H:

You'll then need to set up your Speedlite(s) as a remote flash. To do this, (a) switch the flash on, (b) press and hold the Zoom button for two seconds, and (c) if required, set the slave ID/group:

CONCLUSION

The ST-E2 transmitter has two clear advantages: (a) it allows photographers to use one or more flashguns off-camera for better results and (b) it sets the correct flash exposure in E-TTL mode.

The disadvantages are (a) its cost, approximately £150 plus battery, and (b) the fact that the Speedlite flashgun must be in the line of site of the ST-E2 transmitter or the signal able to bounce off walls indoors.

Have you tried to determine the maximum range? I'd be interested to know the range indoors and outdoors.

I guess we'll just assume the reported range is correct. So that's 8m outdoors and 12m indoors. Not too shabby, but I guess that will degrade depending on how bright the sunlight is.

Apologies for not responding earlier but I've been very busy. However, I just did a test outdoors and am most surprised by the result. Here's a shot at 8m where I focused on the light stand, and not my son who scootered into view:

I then took more shots at 1m intervals until I reached 19m and had to stop because I ran out of space!

I'll repeat the test as soon as I get a chance on a long stretch of road.